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Rice grown anywhere in the world soon could be made completely flood-tolerant because of new research by University of California Riverside geneticists, done in collaboration with scientists at UC Davis and the International Rice Research Institute in the Philippines. By gradually introducing into California rice "submergence tolerance," a property that enables rice to survive extreme flood conditions, the researchers show how potentially any variety of rice could be made to survive short-term floods that completely submerge the rice plant – a result benefiting rice farmers worldwide.

The researchers are the first to identify a small cluster of related genes responsible for providing a line of Indian rice with the capacity to survive complete submergence for more than two weeks. The researchers transferred this cluster of genes into California rice by first cross-pollinating the Indian and California rice and then continuing the cross breeding over several generations until all the Indian rice genes, except the cluster of genes needed for submergence tolerance, were gradually replaced with genes from the California rice. The result was California rice that can withstand floods in which the rice plant is completely submerged.

Study results appear in this month’s issue of The Plant Cell.

In their work, led by Julia Bailey-Serres, a professor of genetics at UCR, the researchers evaluate two nearly genetically identical lines of California rice: the original submergence intolerant line and the new submergence tolerant line. A careful comparison of the two California rice lines showed that in the submergence tolerant line the rice plants orchestrate a number of cellular responses to submergence that are controlled by specific genes present in the submergence gene cluster. The researchers report that this cluster, which originated in the Indian rice and was bred into the California rice, is responsible for changes in cell metabolism and growth while the plant is submerged.

"One of the genes in the submergence gene cluster makes rice conserve the carbohydrate reserves in the plant leaves when the plant is submerged, resulting in a controlled growth for the plant," said Bailey-Serres, who is a member of UCR’s Center for Plant Cell Biology. "Rice plants that lack this particular gene, however, are not able to conserve their carbohydrates. They end up with accelerated growth and ultimately exhaust themselves."

Flooding of croplands is a frequent natural disaster in many regions of the world, reducing crop productivity. While rice, the primary food for more than 3 billion people, thrives in standing water, it dies if it is completely submerged for more than four days. Water covering the rice plant reduces the plant’s oxygen and carbon dioxide supplies, affecting photosynthesis and respiration. Submerged, the plants lack the gases needed to produce sugar for cellular energy, resulting in death if submergence persists beyond four days.

Bailey-Serres notes that access today to information about the rice genome – all the genetic material in the chromosomes of rice – has greatly accelerated progress in identifying specific genes that confer specific traits. “Currently, the International Rice Research Institute is actively crossing the submergence tolerant Indian rice with lines of rice that are widely grown in southeast Asia in order to produce new lines of rice that can grow in flood-prone areas,” she said.

In the future, Bailey-Serres and colleagues plan to work on developing crops that are resistant to multiple stresses. "For example, we’d like to develop rice that is both submergence and salt tolerant," she said, "given that many flood-prone areas are a mixture of fresh and salt water."

Besides Bailey-Serres, Takeshi Fukao of UCR; and Kenong Xu and Pamela C. Ronald of UC Davis collaborated on the study, which was funded by grants from the United States Department of Agriculture and the United States Agency for International Development. Fukao is the first author of the research paper.

The Center for Plant Cell Biology is the nation's first research center devoted exclusively to plant cell biology. Involving an interdisciplinary effort by engineers, plant biologists, plant pathologists, chemists, physicists and computer scientists, the center seeks to develop a comprehensive understanding of how plants function as whole organisms. Researchers at the center address significant outstanding questions in plant biology by integrating genomic, bioinformatic, cellular, molecular, biochemical, and genetic approaches. For more information, visit www.cepceb.ucr.edu.